1. Field of the Invention
This invention relates to agricultural equipment and, more particularly, to an apparatus to be advanced by a vehicle to continuously produce a visible mark in underlying soil to provide a frame of reference for the vehicle driver.
2. Background Art
In conventional tilling processes, soil is uniformly treated throughout an entire field that is to be planted. Residue from a prior year's crop is broken up and mixed with the soil. Subsequently, a towing vehicle draws soil additive and planting equipment over the tilled soil to produce evenly spaced planting rows.
The first pass over the filled soil dictates the row orientation. The vehicle operator thereafter guides the vehicle by making visual reference to the line of the previously planted rows to ideally produce uniform spacing of rows throughout a field.
This is a relatively inconvenient process in that it requires the operator to divide his/her attention between the front of the vehicle, to avoid any obstructions, and the back of the vehicle, to be certain that the line of the rows in process remains parallel to, and spaced the desired distance from, existing rows. This back and forth movement may cause operator fatigue. While with some crops row placement accuracy is not critical, those crops planted using a grain "drill " i.e. wheat, beans, etc., are normally spaced sufficiently close together that deviation from the desired row spacing may cause a significant decrease in the crop yield.
It is also known to advance a marker through underlying soil as the vehicle is advanced. Typically, the marker projects laterally from the vehicle, or an attachment being drawn thereby, to be dragged through the soil to produce a gauge line as seed is planted or additive applied. After the initial pass, the operator can steer off of this gauge line while looking forwardly as he/she would in normally operating the vehicle.
However, when modem tilling techniques are utilized, other problems arise which must be contended with even when a marker is employed. There has been a growing concern about preserving top soil, which can be done by at all times leaving a blanket of residue on the soil between rows. Whereas these "no till" techniques were once optional, the U.S. government is now requiring that top soil remain at all times intact over a certain portion of active fields.
As a result, the wheel producing the marks must be dragged through residue, rather than cleared, loosened soil. Less than a clearly defined mark may result with conventional markers.
This problem can be alleviated to a certain extent by utilizing a heavier marker or skewing the wheel axis so that the wheel is caused to dig a wider trough, which serves as the marking line. However, by increasing the down pressure on the wheel or increasing the resistance to passage through the soil by increasing the width of the mark, the structure supporting the wheel may become severely stressed. As a result, a heavier than desirable construction may be required, which adds to the cost of the marker and may complicate repositioning and folding of the marking structure, which takes place when the towing vehicle is being transported from site to site or reconfigured for storage.
One type of conventional marker utilizes an elongate boom, which projects in cantilever fashion from the towing vehicle. A rotatable wheel is provided on the distal end of the boom. The wheel is self propelled as it is dragged through the underlying soil. The wheel orientation can be varied from a position wherein the axis thereof is substantially parallel to the length of the boom, which produces a very narrow cut in the soil, to a position wherein the axis makes a substantial angle with the boom length, so that a relatively wide trough is formed in the soil.
Many existing markers are constructed with a "breakaway feature". Part or all of the boom is constructed to reposition upon a predetermined force being applied thereto, as when an obstruction is encountered by the wheel. This avoids damage to the marker and the equipment to which the marker is attached.
Some of these markers utilize bolts which are severed in shear upon a predetermined force being applied to the distal end of the boom. Markers utilizing this arrangement may have less than consistent performance. In normal use, the shear pin or bolt may progressively wear away so that it becomes weakened to the point that it will fail prematurely or under a force that is less than the desired breakaway force.
This shear arrangement is also less predictable than desired in light of the number of variables that are involved. For example, sharp comers on two elements moving in shear may effect shearing of the pin/bolt at a lesser force than would elements having more rounded edges.
It is also known to utilize a pin/bolt that is designed to fail in tension upon the wheel encountering a predetermined resistance. In one form, a vertically extending pin extends through cooperating knuckles at the trailing end of two boom portions so that the outermost portion with the wheel thereon can pivot towards the vehicle, as upon encountering an obstruction. The tension bolt/pin extends through plates at a location forwardly of the boom. The bolt/pin is aligned with the length of the boom so that the hinge bolt/pin at the rear portion of the body of the boom serves as a fulcrum to convert the rearward force on the wheel into substantially an axial force on the bolt/pin.
With this arrangement, the tension pin/bolt is substantially aligned with the neutral axis of the boom. As a result, it does not significantly resist bending loads applied to the boom in use. Further, in those apparatus in which the boom can be raised and/or folded, the lifting force is transmitted primarily through the hinge pin i.e. the tension bolt/pin does not significantly rigidify the boom.
Another problem with the conventional arrangement described above is that separate boom configurations must be made for right- and left-handed use so that the pivot axis is properly located in a trailing position on the boom. Since many markers are retrofit to existing equipment, this is potentially inconvenient for the user and requires that the manufacturer keep an inventory of anticipated left- and right-handed markers. In the case of the user, the user may want to mark on only one side at a time. He/she must nonetheless purchase a right- and left-handed marker to have the ability to mark on both sides.